I am currently involved in an ITIL assessment to "move up the value chain" of the project i.e. from Level 1 - Staff Aug to Level 3 - Managed Services

I wanted to know if there was a threshold defined for ITIL lifecycle areas at different maturity levels. Example :
At level 2(Call it service delivery) ,
Service Strategy is at 0%
Service Operation is at 50%
Service Design is at50%
Service Transition is at 25%
CI is at 25%

Likewise for other maturity levels.
In summary, for the above mentioned parameters, what compliance ratio must be reached (25%, 75%, 100%, ...)so that it qualifies for the next level

In consequence of the indisputable assertions made by John, "ITIL assessment" is an artificial concept and any such assessment allegedly performed, will be loaded with value judgements and therefore can be made to seem anything at all.

There are two practical approaches that might meet your requirements.

The first is to conduct a quality audit against ISO20000. It doesn't matter that you may "fail". All you are interested in is the identification of areas for improvement which the audit report should draw out. The down side will be if your management system is too far away from the standard, then you will drown in the outcomes and struggle to identify the way forward.

The second approach is to identify your areas of greatest concern and begin to tackle them through an ongoing improvement program. The downside here is if you have very little useful quantitative data concerning your present state then you will not be able to measure your improvements or even prove that they are. However you can deal with this by having an initial phase that begins to put in place the activities to collect useful data. This will be an improvement, but will not of itself improve your service delivery.

In either of these approaches you can use your understanding of the ITIL guidance to inform your improvements.

You can of course conduct some kind of maturity assessment based on one of several documents I believe to be out there somewhere. but such things are always fairly subjective and I would suggest you just did a quick once over if you felt it might get you started. If you take these too seriously you could find yourself devoting more effort to improving your maturity than improving your services._________________"Method goes far to prevent trouble in business: for it makes the task easy, hinders confusion, saves abundance of time, and instructs those that have business depending, both what to do and what to hope."
William Penn 1644-1718